Electronically controlled fuel pump

ABSTRACT

The disclosure illustrates an electronically controlled fuel pump in which a bypass valve regulates its output pressure to a predetermined level above a control pressure. A downstream throttling valve re-regulates the pressure to a predetermined level below a control pressure. The control pressure is established by an electro-hydraulic valve which is, in turn, fed with signals with a microprocessor to provide appropriate control. The use of the control pressure in effect causes a servo action and utilizes the pressure of the fuel to manipulate the valve and minimize the power requirement of the electro-hydraulic valve.

The present invention relates to fuel pumps and more specifically fuelpumps for internal combustion engines of the compression ignition type.

One of the fundamental requirements for a compression ignition (diesel)internal combustion engine is the provision of a fuel injection systemthat provides a precisely metered and quantity of fuel at the correctmoment in the compression cycle to provide ignition of the resultantmixture. In the past, this control has been done using various forms ofhydro-mechanical systems. One such system is the PT fuel system producedand manufactured by Cummins Engine Company, Inc. and disclosed in U.S.Pat. Nos. 2,727,503 and 2,749,897. In this system, a series of unitinjectors are located at the cylinder head and are cam actuated toinject into the combustion chamber, quantities of fuel that have beenmetered into the injector as a function of the fuel pressure existingupstream of a fuel injector metering orifice. The system utilizes a fuelpump which provides the pressure at the injector to produce the meteredquantity of fuel as a function of operator demand, engine rpm andmanifold pressure.

The problem in a system of this type is that the control functions whichare to be achieved by the fuel pump are closely tied together, therebylimiting flexibility. The control functions may be summarized as asensing function, a computing function and an action function. In thehydro-mechanical system, the sensing function if, for example, rpm isdone by a pair of flyweights on a rotatable shaft assembly and theflyweights also act to compute the force on a spool valve which providesthe action to be taken, namely variably restricting fuel flow to achievethe desired pressure output. Such a system is cost effective but lacksthe ability to utilize diverse parameter inputs to provide a mosteffective control of pressure to meet efficiency and emmission goals.

In the prior art hydro-mechanical fuel systems as exemplified by U.S.Pat. Nos. 2,727,503 and 2,749,897, the pressure required at the injectorruns from relatively low pressures of 1/2 to 1 psi to a maximum of 250psi. Consequently, the power required to manipulate the pressure isextremely great and is not able to be done directly by commonly knownelectronic devices. Furthermore, in such a prior art system the pressureof a simple gear pump is regulated to a constant, very high level andthen selected portions of this are bled off to provide the variablepressure necessary at the injector. The problem with such a system isthat the increased load on the gear pump would tend to reduce its longterm life.

In accordance with the present invention the above problems are solvedin a fuel system for an internal combustion engine of the above generaltype by a fuel pump which comprises pump means for pressurizing a sourceof fuel and electronic control means for generating an electrical signalas a function of selected control inputs. A means is provided forregulating the output pressure of the pump means including a meansresponsive to the electrical signal for establishing a control pressureand a means responsive to the control pressure for regulating the supplypressure of the pump means to a predetermined level above the controlpressure. Finally a means responsive to the control pressure is providedfor re-regulating the supply pressure of the pump means to a fuel pumpoutput pressure that is a predetermined level below the control pressurewhereby the degree to which the output of the pump means is pressurizedis minimized.

The above and other related features of the invention will be apparentfrom a reading of the following description of the disclosure shown inthe accompanying drawings and the novelty thereof pointed out in theappended claims.

In The Drawings:

FIG. 1 is a sectional view of an electronic fuel pump embodying thepresent invention together with the internal combustion engine withwhich it is associated.

FIG. 2 is a schematic drawing of the hydraulic control system along witha schematic drawing of the electronic computation package.

FIG. 3 is a cross-sectional view of the fuel pump of FIG. 1 taken onlines 3--of FIG. 1.

FIG. 4 is another cross-sectional view of the fuel pump of FIG. 1 takenon lines 4--4 of FIG. 1.

Referring to FIG. 1 there is shown a compression engine 10 with whichthe present invention is used. Since its principles of operation arewell known, the complete details of engine 10 will not be covered tosimplify the discussion of the present invention. For the presentdiscussion it is enough to say engine 10 relies on the heat ofcompression of air to ignite fuel that is injected in timed sequence byfuel injectors 12. Injectors 12 are of the direct injection type inwhich a cam actuated plunger injects fuel at high pressure into theengine cylinders (not shown) for combustion.

The exhaust gases from the engine pass across the turbine of aturbocharger 13 which drives its compressor 19 to pressurize air fordelivery through duct 15 to intake manifold 17. Injectors 12 receivefuel from a fuel system 16 via a distribution conduit 14. Fuel system 16receives fuel from a supply line 18 and tank 20 and pressurizes it fordelivery to conduit 14.

The fuel system 16 comprises a fuel pump 22 which comprises a housing150. In order to achieve a clearer understanding the function of thepump will be described in connection with the schematic showing of FIG.2. The key elements of the system will be designated with the samenumbers for FIGS. 1 and 2.

The fuel pump comprises an engine driven pump 26 which may be a gearpump or other positive displacement pump driven by the engine (note themechanical connection thereto) and receiving fuel from a main supplypassage. The output of the pump is discharged into a main passage 28which extends through a throttling valve chamber 30 and an outletpassage 32 which connects with the line 16. A bypass passage 34 extendsfrom the main passage 28 to a valve chamber 36 which has a port 38connected to a drain line 40 extending to a lower pressure area and, ifdesired, to the fuel tank 20. A bypass valve element 42 is positioned inchamber 36 and is urged by a spring 44 in a direction which closes offbypass port 38. In addition, a passage 46 extends to a control pressurepassage 48.

Control pressure passage 48 is connected to the main passage 28 by apassage 50 having an orifice 52 of predetermined size which limits theamount of flow that can pass into control passage 48. Passage 48 extendsto an orifice 54 which discharges into a chamber 56 connected via adrain line 58 to a lower pressure source which may be the tank 20. Anelectro hydraulic valve 60 is positioned to have a valve element 62closely adjacent the orifice 54 so that movement of valve 62 relative toorifice 54 provides the variable opening. Valve element 62 is connectedto a armature 64 positioned within an electromagnet 66 which receivescurrent input signals via line 68 to control the effective area oforifice 54 as a function of an electrical input signal. While manydifferent valves may be employed for this purpose, the electromagneticvalve manufactured by Moog, Inc. of East Aurora, New York 14052 achievessatisfactory results.

A spool valve 70 is contained within chamber 30 for longitudinalmovement and has a land 72 which cooperates with an outlet port 74 toprovide a variable restriction to flow into passage 32 as a function ofthe displacement of spool valve 70. A first end 76 of spool valve 70 isacted on by a spring 78 in a direction to increase the restriction toflow at port 74. In addition, a passage 80 connects with passage 32 toapply the pressure existing in passage 32 to the first end 76 of spoolvalve 70 to also act in a direction increasing the restriction to flow.A second end 82 of spool valve 70 is connected via port 84 to thecontrol pressure passage 48 so that the control pressure existing inpassage 48 acts in a direction which decreases the restriction to flowpast port 74.

The electro-hydraulic valve 60 functions to variably restrict flow outof orifice 54 and thus establish a control pressure which is utilized toestablish an output pressure to make the system function in a manner tobe described later. The signal in line 68 is fed to theelectro-hydraulic valve by a microprocessor circuit generally indicatedat 86 via a connector 88 having a first portion directly connected tothe microprocessor 86 and a second portion 90 connected to line 68.

The microprocessor 86 receives additional electrical control inputs. Forexample, an output fuel pump pressure transducer 92 senses the pressurein passage 32 and generates a signal via line 94 which extends toconnector 96 and then to microprocessor 86 via connector 88. Inaddition, an operator manipulated throttle valve 100 addition downstreamof line 32 has its position factored into the control by a transducer102 connected to the throttle which generates an electrical signal vialine 104 and connector 106 through connector 88 to the microprocessor86. A further control input signal is generated by a magnetic speedsensor 110 which typically sensing passage of a coupling in the input tothe pump 26 and generates a signal via line 112 which extends toconnector 114 on connector 88.

In order to positively terminate flow to the injectors 12 anelectrically actuated solenoid shutdown valve 120 is provided in line32. This valve 120 receives a control input via line 122 from connector124 which in turn connects to one portion of connector 88.

Additional control inputs may be employed to make the microprocessor 86take different parameters into account for its control function. Theseparameters may be generated on the internal combustion engine or theymay be generated in connection with the vehicle powered by the engine.For engine mounted sensors and transducers, a connector 130 iselectrically connected to microprocessor 86 and has various connectors132 which include lines 134 extending to various transducers and controlelements. For vehicle interconnections a connector 136 is directlyelectrically connected to microprocessor 86 and includes correspondingconnector 138 leading to a wire or harness 139 interconnected withvarious vehicle components.

Referring back now to FIG. 1 and to FIGS. 3 and 4, the pump housing 24is comprised of a series of zones which provide for a more efficientarrangement of the component and a more ready access for maintenance.

A first zone 140 includes the supply pump 26 and associatedelectro-hydraulic transducers and control elements. A second zone 142comprises a cavity 144 in which the various transducers and controlelements are mounted and a heat transfer passage 146 to be describedlater.

A third zone 148 comprises the microprocessor 86 and associatedelectrical connectors.

The first zone 140 comprises the housing element 150 in which the pump26 is housed. The input shaft 152 for the pump has a coupling 154 whosemotion past the magnetic sensor 110 provides the rpm input.

As described earlier, the housing 150 also contains the varioushydraulic control elements including the electrohydraulic valve 60 whichis mounted on an end wall 156 of housing 150 and the pressure sensor 92is also mounted on the end wall 156. In addition, the shutdown valve 120is conveniently located on the same end wall 156 (see FIG. 4). Thesecond zone 142 comprises a housing 158 which surrounds the cavity 144.As is apparent from FIG. 1, the various transducers and control elementsare positioned within cavity 144 so that they are protected frommoisture and other adverse elements of the environment. In order to gainaccess to the transducers for replacement, repair or adjustment,housings 150 and 158 are pivotally connected at 160. The housings areheld in the illustrated position by suitable detachable connectors (notshown).

In order that the flexible lines which connect the various elements tothe connector 88 of microprocessor 86 do not experience a change inlength when the housings are pivoted to expose the transducers, thelines 112, 68, 122 and 94 are positioned closely adjacent the pivotpoint.

Housing 158 also contains the cooling passage 146 more particularlyillustrated in FIG. 3. The heat transfer passage 146 comprises a firstwall element 170 integral with housing 158 and a second wall element 172integral with housing 174 for zone 148. The walls 170 and 172 areopposed and spaced from one another and, with particular reference toFIG. 3, an inlet port 176 in end wall 170 connects with inlet passage 18and an outlet port 178 connects with main fuel pump supply passage 25.

The fuel flowing from the inlet to the outlet port is made to travel atortuous path by a barrier which bridges a substantial portion of thespace between the walls and which comprises a longitudinal straightsection 180 extending from a point in between ports 176 and 78 and to aremote point adjacent the other end of the wall where a bend section 182causes the fuel to be diverted generally at a right angle to thelongitudinal barrier 180. An additional barrier 184 integral with aperimeter wall 186 extends generally laterally with respect tolongitudinal barrier 180 to cause the fuel to achieve an "s" shapepattern. Another lateral barrier element 188 extends from thelongitudinal barrier 180 at a point adjacent the outlet port to force afinal change of direction before the fuel exits through port 25 and intothe inlet of the pump.

An auxiliary outlet passage 190 in wall 170 adjacent outlet port 178connects with a passage 192 leading to an electrically actuatedauxiliary pump 194 which discharges its output by a line 196 to asuitable drain, preferably the fuel tank 20. The pump 194 isthermostatically actuated and responds to a temperature sensor (notshown) in the microprocessor 86 to begin pumping whenever thetemperature exceeds a predetermined maximum.

The final zone in the pump is 148 which comprises the housing 174 inwhich a pair of circuit boards 200,202 are positioned. Circuit boards200,202 comprise various electronic control elements including powergenerating elements 204. These power generating elements 204 haveintegral heat sinks 206 associated therewith to dissipate the heatgenerated by them. These heat sink elements are structurally connectedto the wall 172 which is heat conductive and to a cover 208 which isalso heat conductive. As a result, a direct path for heat by conductionis provided from the power generating elements 204 to the respectiveheat conductive walls. Since wall 172 is exposed on one side to the fuelflowing by it effectively takes the heat away from the circuit boards.The circuit boards are maintained in place and protected from vibrationby a suitable potting material (not shown). The connectors referred tobefore are directly connected to the circuit boards 200,204 and havetheir interface extending through the wall of housing 174 to provideconvenient connection to the exterior.

During operation of the fuel system described above the pump 26 isdriven to pressurize fuel and pull it from main supply conduit 25 pastthe heat exchange assembly 146 to thus provide a cooling function forthe microprocessors 86. It is noted that the fuel temperature, in mostcases, is maintained below 150° F. which is well within theenvironmental limits of the microprocessor. The flow that passes fromthe pump is bypassed by the valve element 42 to maintain a pressurewhich is a fixed differential above the pressure existing in line 48.This fixed differential is generally established by the spring constantof spring 44.

The regulated pressure in line 28 is essentially re-regulated bythrottling past the spool valve 30. This spool valve maintains thepressure downstream of it at a fixed differential below the pressureexisting in line 48. In a similar fashion the spring constant of spring78 establishes the amount of the pressure differential.

Thus we see that the pressures both relate to the control pressure inline 48. Because of the orifice 52, the flow into passage 48 is limitedand since the wide open area of orifice 54 is greater than orifice 52, apressure that is lower than in the line 28 can be established in passage48. This pressure therefore is manipulated up or down to meetrequirements set by the microprocessor 86. The output pressure in line32 therefore is at the appropriate pressure for the use by theinjectors. The pressure head against which the pump 26 must act is onlya predetermined level above the control pressure. Since the duty cycleof an engine requires pressure generally below the maximum obtainablepressure, it can be seen that the overall pressure to which the pump issubjected is substantially reduced.

During shutdown there are conditions when the engine experiences greatlyelevated temperatures, for example, after a heavy duty operating cycleduring a hot ambient day. In this case temperatures can go over 200°.Whenever a temperature of a predetermined maximum, for example 180°, inthe microprocessor is exceeded, the auxiliary pump 194 is actuated todischarge fuel from the cooling assembly 146 adjacent the outlet port178. This causes fuel to be drawn into the inlet port 18 and through theheat exchanged passage and back to the tank thus cooling themicroprocessor and maintaining its temperature at an acceptable level.

The circuit boards forming the basic part of the microprocessor areconnected in place through the heat sink elements and the connectors inorder to achieve a sturdy mounting and protect them from vibration. Inaddition, the direct connection through the heat sinks enhances the heatflow to the heat exchanged portion.

The accessibility of the transducers and other elements that wouldrequire periodic maintenane, replacement or adjustments is enhanced bythe pivotal connection and the placement of the lines so as to minimizethe stress placed on them during this operation.

While the invention has been described in connection with a preferredembodiment it should be apparent to those skilled in the art that it maybe practiced in forms other than those specifically described withoutdeparting from its spirit and scope.

Having thus described the invention, what is claimed as novel anddesired to be secured by Letters Patent of the United States is:
 1. In afuel system for an internal combustion engine having injectors whichmeter fuel to said engine as a direct function of fuel pressure, a fuelpump comprising,pump means for pressurizing a source of fuel, electroniccontrol means for generating an electrical signal as a function ofselected control inputs, and means for regulating the output pressure ofsaid pump means comprising, means responsive to said electrical signalfor establishing a control pressure, means responsive to the controlpressure for regulating the supply pressure of said pump means to apredetermined level above the control pressure; and means responsive tothe control pressure for further regulating the regulated supplypressure to a predetermined output level below the control pressure,said fuel pump outlet pressure level being the level necessary foroperation of the injectors, whereby excessive pressurization of the pumpoutput is minimized.
 2. Apparatus as in claim 1 wherein:said fuel pumpcomprises means for establishing a main passage from said pump means tothe output of said fuel pump; said control pressure means comprisespassage means for providing a predetermined bleed flow from said mainpassage to a lower pressure drain and electrically responsive variableorifice means for variably restricting the flow through said bleed flowpassage means as a direct function of an electrical input whereby thecontrol pressure is a direct function of electrical input.
 3. Apparatusas in claim 2 wherein:said bleed passage means comprises a passageextending from said main passage and including a fixed orifice ofpredetermined size; said variable orifice means comprises a drainorifice downstream of said fixed orifice and an electrically operatedvalve assembly that variably restricts the flow from said drain orifice.4. Apparatus as in claim 3 wherein:said electrically operated valveassembly comprises a movable armature having an element connectedthereto that variably restricts said drain orifice and an electromagnetresponsive to a current input.
 5. Apparatus as in claim 2 wherein:saidsupply pressure regulating means comprises means for variably bypassingthe output of the pump means to the lower pressure drain as a functionof said control pressure, and said fuel pump output regulating meanscomprises means for variably throttling the main passage as a functionof said control pressure.
 6. Apparatus as in claim 5 wherein:saidvariable bypass means comprises means for establishing a bypass passagefrom said main passage to said lower pressure drain and a valve elementdisplaceable in said bypass passage means for variably restricting flowtherethrough, the valve element being positioned to have one facethereof exposed to pressure in said main passage so that said pressureurges the valve element in a direction which increases the flow throughsaid bypass passage and means for urging said valve element in adirection which decreases flow through said bypass passage, said urgingmeans comprises a yieldable urging means and means for connecting thevalve element to said control pressure.
 7. Apparatus as in claim 6wherein said fuel pump output regulating means comprises:a spool valvepositioned in said main passage and having one land thereof registeringwith said main passage for variably restricting flow therethrough as afunction of the displacement of said spool valve; means for applying thefuel pump output pressure to a first end of said spool valve, so as tourge said spool valve in a direction increasing the restriction in saidmain passage; yieldable urging means acting on said first end to add tothe urging force of said fuel pump output pressure; means for applyingthe control pressure to the second end of said spool valve so as to urgesaid spool valve in a direction decreasing the restriction in said mainpassage.